June 25, 2008

8,700 year old clock gene selected in non-Africans

Genetic diversity patterns at the human clock gene period 2 are suggestive of population-specific positive selection

Fulvio Cruciani et al.

Abstract

Period 2 (PER2) is a key component of the mammalian circadian clock machinery. In humans, genetic variation of clock genes or chronic disturbance of circadian rhythmicity has been implied in the onset of several phenotypes, ranging from periodic insomnias to advanced or delayed sleep phases, to more severe disorders. Peculiar geographic diversity patterns in circadian genes might represent an adaptive response to different light/dark cycles or environmental changes to which different human populations are exposed. To investigate the degree and nature of PER2 gene variation in human populations of different geographic origin, and its possible correlation with different latitudes, we sequenced a 7.7 kb portion of the gene in 20 individuals worldwide. In total, 25 variable sites were identified. The geographic distribution of haplotypes defined by five polymorphic sites was analyzed in 499 individuals from 11 populations from four continents. No evidence for latitude-driven selective effects on PER2 genetic variability was found. However, a high and significant difference in the geographic distribution of PER2 polymorphisms was observed between Africans and non-Africans, suggesting a history of geographically restricted natural selection at this locus. In support of this notion, we found several signals for selection in the sequences. The putative selected haplotype showed a recent coalescent age (8.7 Kyr), and an unusually high frequency in non-African populations. Overall, these findings indicate that a human clock-relevant gene, PER2, might have been influenced by positive selection, and offer preliminary insights into the evolution of this functional class of genes.

How all this selection might be reflected in phenotype is a good question.

A study in P&ID found that there was a significant circadian phase shift at adolescence - such that more people begin to prefer eveningness over morningness. Although the sample sizes were low they found that "Hispanic children change least with age in their morningness–eveningness preference whereas African American children change most. For both Asian and Caucasian children, the degree of change in their morningness–eveningness preference seems to fall in the middle relative to Hispanic and African American children, and the patterns of change appear to be similar to each other."

"There are remarkable racial differences in reported napping and nighttime sleep patterns beginning as early as age 3 and extending to at least 8 years of age. These differences are independent of commonly investigated demographic factors... At age 8, 39.1% of black children were reported to nap, compared with only 4.9% of white children. Black children also napped significantly more days per week, had shorter average nocturnal sleep durations, and slept significantly less on weekdays than on weekend nights."

So the idea is that the smarter you are, or at least the bigger your brain (this does not perfectly correlate with IQ) the longer REM sleep you need?

Its interesting, a long time ago, I read about Einstein's life and he was known to sleep a lot, take naps in. Bruce Lee also promoted sleeping a lot, but then again we know little about his intelligence and he had a ridiculous workout schedule, the guy must have had a huge metabolism and the article Jason posted said that animals with high metabolisms for their size sleep more as well.

I wonder is there a link between having a high metabolism for your size and intelligence?

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